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20 October 2013

BOBGRAM issued 20 Oct 2013

WEATHERGRAM
YOTREPS
Issued 20 October 2013
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

The Palolo are rising
For those lingering in the South Pacific until the end of the month : you may be in for an interesting delight this weekend with the waning moon, especially around the third quarter- when the tide starts ebbing just before dawn. In October or November this usually triggers a spawning of a coral worm called Palolo (or Balolo in Fijian). Sometimes this may be large enough to colour the sea – stuff can be netted and eaten raw or cooked. Ask the locals.

The South Pacific cyclone season:
The scientists in NZ, Fiji and Australia have issued a report about what to expect in the South Pacific for the cyclone season Nov 2013 to April 2014. They expect a near average numbers over the region as a whole (8 to 12), with increased activity late in the season.

TROPICAL TOPICS
Things remain busy in the Northern Hemisphere tropics with TC FRANCISCO skirting southern Japan. TC RAYMOND is off the west coast of North America and is not expected to make landfall. . Tropical depressions 01F and 02F, the first two of this new season, are being watched by the Fiji Met Service tonight. More about them soon.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is activating so that TD01F has appeared on it between Solomons and northern Vanuatu as an open trough area. Also TD02F has appeared as a closed isobar centre to southwest of Funafuti. TD01F is expected to fade away on Monday and TD02F is expected to go S and SE then convert into a dose of very squally weather moving across Fiji on around Tuesday 22 Oct UTC. It is the expected to take an active part of the SPCZ onto Tonga on Thursday and Friday UTC and then onto Niue on Saturday/Sunday UTC. Avoid.
During Sat/Sun the trough near Niue is expected to link with a front from NZ and form a large slack trough of light winds over the Kermadecs area
Another branch of the SPCZ is lingering along 5 to 8S across Northern Cooks.

Sub-tropical Ridge STR
The STR is expected to remain strong along 30 to 32S this week, and that means enhanced trade winds on the north end of the traveling highs.
One high is expected to move east along 32S from NZ to 120W between Monday and Friday.

The next High is expected move from Australian on Saturday 16 Oct across the Tasman Sea at 33S and then the North Island by Tue/Wed 29/30 Oct.

NZ/Tasman Sea
This area continues to have periods of unsettled weather with enhanced winds south of 35S, especially in between the high cells of the STR. Thursday 24 to Monday 28 Oct is expected to be one of these periods, right in time for Labour week- a long holiday weekend celebrated in NZ. A front is expected to cross northern NZ on Friday night, proving an interesting challenge to those involved in this year's Coastal Classic from Auckland to Russell in the Bay of Islands. This front is expected to be followed by W/SW winds until late on the holiday Monday, good for the return home.

Route Briefings
Tahiti to Tonga:
A trough is lingering to east of Tahiti at present but should fade. The STR is maintaining useful trade-winds all the way to Tonga at present, but that trough reaching Niue on Sat/Sun 26/27 UTC may change this.

Between tropics and NZ
Looking OK to depart when the SPCZ in not visiting. For Fiji this is on Wednesday/Thursday/Friday, and from Tonga this is Monday /Tuesday/part of Wednesday.
After the SPCZ visits Tonga on Thursday and Friday a large slack trough is expected to form near the Kermadecs and that may delay departures from Tonga for a while.
Avoid arriving in New Zealand when a front crosses on Friday 25 UTC or the next front on Thursday 31 Oct.

Between New Caledonia and Australia
A trough is expected to be crossing the eastern seaboard of Australia around Tue/Wed/Thu 22/23/24 and another on Tue/Wed 29/30 Oct. Avoid arriving on these dates.